In recent years, flat panel display devices that use flat panel display elements such as liquid crystal panels and plasma display panels are increasingly used as display elements for image display devices such as television receivers instead of conventional cathode-ray tube displays, allowing image display devices to be made thinner. Liquid crystal panels used in liquid crystal display devices do not emit light on their own; therefore, it is necessary to provide a separate backlight device as an illumination device.
One known type of backlight device is a direct-lit type backlight device in which light is directly supplied to the liquid crystal panel from the rear surface thereof. In such a direct-lit type backlight device, a light source substrate having light sources such as LEDs disposed thereon is attached to a bottom plate of a chassis that is used as a case. Through holes for allowing the pins that secure the light source substrate to go through are formed on the light source substrate, and through holes are also formed at locations on the bottom plate of the chassis that face these through holes. The light source substrate is secured by the pins going through the through holes formed on the light source substrate and the through holes formed on the bottom plate. One light source substrate is secured by a plurality of pins. Patent Document 1 discloses a conventional example of such a direct-lit backlight device.